1997 Ford Expedition On Expedition Put Aftermarket Radio Powers Gets Sound

On my 1997 ford expedition. I put in a aftermarket radio.it powers up but it gets no sound .i heard someone say that it was the factory amp causing the problem. They also said they bypassed it by using the remote wire from the aftermarket radio. By using that it turned the amp on. So two things were is the factory amp in the truck. And what color wire do I use on the factory amp to power it up.
Thank you jeff